GIS in Management Planning. Lab 2 Coordinate Systems and Map Projections

Transcription

1 GIS in Management Planning Lab 2 Coordinate Systems and Map Projections Tomislav Sapic GIS Technologist Faculty of Natural Resources Management Lakehead University

2 ArcGIS ArcToolbox Projections Functions The Define Projection function in ArcToolbox (Data Management Tools Projections and Transformations Feature or Raster ) is used to define projections of both, vector and raster datasets. Within the Define Projection function, the Modify setting is used to, among other things, correct y and x shifts. A dataset must have its map projection defined in order for ArcGIS to project it into another map projection. The Project function in ArcToolbox (Data Management Tools Projections and Transformations Feature or Raster ) is used to project datasets -- vector files in the Feature box and rasters in the Raster box.

3 ArcGIS - Define Projection Input dataset (e.g. shapefile) Coordinate system of the input dataset. Examples Select Geographic coordinate system World Projected coordinate system Utm WGS 1984 Nad 1983 NAD 1983 UTM Zone 16N

4 Input dataset (e.g. shapefile) ArcGIS - Project Output dataset (e.g. shapefile) Coordinate system into which the output dataset is projected. Examples Select Geographic Transformation has to be used when the datums between the input and output differ. Geographic Coordinate Systems World WGS 1984 Projected Coordinate Systems Continental North America The invalid sign in the Project function window can mean two things: a) The input dataset doesn t have a defined projection b) You need to close your ArcMap project (if using ArcToolbox from ArcCatalog) and/or refresh the folder in ArcCatalog where the input dataset is located Canada Lambert Conformal Conic

5 ArcMap Data Frame s Coordinate System (Map Projection) Data Frame -- the platform that holds layers in ArcMap, by default named Layers, and sets the coordinate system in which all layers are displayed. Data Frame s coordinate system gets set by the first layer that is added to ArcMap but can later be changed to a different coordinate system.. Layers representing GIS datasets with defined projections that differ from the Data Frame s map projection, get projected on-the-fly into the Data Frame s projection. If the first layer s map projection is undefined, the Data Frame s coordinate system gets set to Unknown and the layer is displayed by its features coordinates. In such case all other added layers have their map projection disregarded and get displayed within the coordinate system of the first layer s features.

6 Data Frame s Coordinate System Data Frame s projection can be changed from one projection into another one: right click on the data frame>properties >Coordinate System, use the coordinate system of one of the layers or select a different one from either Projected Coordinate Systems or Geographic Coordinate Systems folders. Layers representing GIS datasets whose coordinate system is undefined are listed as having an Unknown coordinate system. They don t get projected on-the-fly and are displayed within the Data Frame s coordinate system directly based on the coordinates of their features. This works if the features are in the same coordinate system as the set Data Frame s coordinate system, and it doesn t if they are not. If the data frame contains layers in different datums (e.g. WGS84 and NAD83), a transformation model has to be specified.

7 A dataset s features true coordinates are best seen in ArcCatalog s Preview tab. Because ArcMap projects on-the-fly the coordinates seen in it can belong to a coordinate system that differs from the dataset s. x, y coordinate of the cursor s position within the dataset s coordinate system

8 Dataset Projections in ArcGIS ArcMap Information on a particular dataset s projection (projected coordinate system) can be found in ArcMap by going into the layer s properties (right-click on the layer), Source tab, and in ArcCatalog by either right-clicking on the dataset and going to Properties > XY Coordinate System tab, or by selecting the layer and looking under the Description tab, in the Spatial Reference section. ArcCatalog

9 How to Add a Basemap Image to ArcMap 1) Click on Add Data, choose Add Basemap 2) Pick one of the basemaps. 3) Once the basemap image is displayed, go to Data Frame and set its coordinate system to the basemap s, in the Layers folder. Point 3 doesn t have to be performed but it does speed up the display of the basemap.

10 Additional Sources: Ilifee J. and R. Lott Datums and Map Projections: For Remote Sensing, GIS and Surveying. Whittles Publishing. Furuti C. A Cartographical Map Projections. (January 20, 2011) ArcGIS 9.3 Help About Map Projections. map_projections (January 20, 2011)